This research was initiated by the general impression of the authors that elementary and secondary school pupils showed a different success rate in the acquisition of mathematical knowledge during the post war school year 1999/2000, compared to the recent previous pre-war school years. As the Ministry of Education Federal Republic of Yugoslavia, in that time, proclaimed the end of the official school year, on March 25th 1999, because of the NATO air strikes, the curriculum could not be completed. The NATO strikes on Federal Republic of Yugoslavia lasted from March 23rd to June 9th 1999. In this paper we focused our attention on the two factors that contributed to the lower success in mathematics in the next school year, 1999/2000, at the elementary and the secondary school levels: the organization of the teaching process and psychological problems, both implied by the war events.